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A wise shark knows when to shut up

BASKING sharks know when to keep their mouths shut as they cruise around the
coast, according to a biologist in Britain.

The gentle giants filter tiny plankton from seawater, but their gaping mouths
increase drag. David Sims of the University of Aberdeen calculated that the
sharks should keep their mouths shut when there is less than 0.55 grams of
plankton per cubic metre. Below this, the animals would not recoup the extra
energy needed to swim with an open mouth.

Tracking a feeding group of the fish, Sims found that their behaviour matched
his model (Proceedings of the Royal Society B, vol 266, p 1437).